Technological Field
The present disclosure relates to a method and a device for calculating an indication of power of a received radio signal.
Description of the Related Technology
In communication using radio technology, there is often a need or desire to determine the signal strength. For instance, in many communication standards, such as ZigBee®, Wi-SUN®, and Bluetooth® Low Energy (BTLE), Received Signal Strength Indicator (RSSI) and Clear Channel Assessment (CCA) are mandatory functionalities at physical layer level for supporting Logical Link Control (LLC) and Media Access Control (MAC). The functionalities may require that an average power for a given time interval is determined. Thus, the power of the radio signal in a specific frequency channel for a specific amount of time may need to be measured, so that the average power may be calculated.
Selecting a specific frequency channel may be realized in digital baseband, which implies that the average power or a related value or measure needs to be determined in digital domain. Further, the average power may be determined based on a sum of squares of the measured powers.
However, a digital average power detector may set extensive requirements, in terms of area and power demands, when a large number of digital values are to be summed, in particular if the numbers are to be squared before summing.
In U.S. Pat. No. 5,944,774, a method is disclosed for performing calculations on numbers expressed as logarithmic values. The method seeks to reduce the effort involved in adding or accumulating a large number of digital logarithmic values. The method is based on realization that logarithmic quantities are preferably not combined in order “smallest plus largest,” since the contribution of the smallest number will disappear in the logarithmic representation of the sum. Instead, the two smallest quantities are preferably combined together first to produce a sum which is larger than each of the two quantities. The sum is preferably re-sorted in descending order of value with the remaining quantities to be summed and the two smallest quantities again combined and so forth until there are only two quantities left to combine, for example, the largest quantity and the sum of all the others.
However, the method of U.S. Pat. No. 5,944,774 requires that the logarithmic values are sorted before summation may be started and the partial sums re-sorted during summation. Hence, the sorting consumes time, power, memory and/or area.